The second option which does not require dramatic changes to the roof is to do the above and add dormer windows. This will increase the useable floorspace and can be used to add head height which gives you more options when it comes to placement of the stairs.

This will cost upwards of £25,000. However the average dormer loft conversion with a double bedroom and en suite costs about £35,000–£45,000.

Loft Conversions Which Involve ‘Raising the Roof’ or Changing the Roof Structure

This option is the most expensive as it require the removal and rebuild of the existing roof. It also requires planning permission approval so you local planning permission application cost must be added on. Another added expense will be the additional design work that may be needed as it is more complicated that a room in roof, or dormer loft conversion. This type of work is likely to cost upwards of £40,000. Some companies will create a package type ready-made room which is fabricated off-site and craned into position. The benefit of this is that it is quicker than replacing the rafters and rebuilding the roof thus reducing scaffold hire and labour costs. However, this option costs around £55,000 for the average home.